The present invention relates in general to telephone voice communication networks, more particularly, it relates to an local area computer network capable of delivering telephone services.
A typical modern office building provides each worker with their own telephone. Rather than purchasing all the required telephone lines from the local telephone company, most offices have established their own private telephone networks. The private telephone network can handle calls originating and terminating within the building without going through the public switched telephone network (PSTN) provided by the telephone companies. Thus, an office building need only purchase a smaller number of access lines or trunks to connect its private telephone network to the PSTN. Such private telephone networks are commonly known as Private Branch Exchanges (PBXs).
In addition to a PBX, a modern office typically has a number of personal computers (PCs) connected by a local area network (LAN). The PC LAN connects together the PCs in the office to share data, printers or other computer peripheral hardware. Although many different PC LAN configurations are possible, each PC on the network is typically connected via a connecting medium to one or more central hubs or switches which allow communication between network nodes. A primary computer or file server typically stores a large quantity of data and implements a data transmission control protocol to arbitrate the distribution of data over the network.
Traditionally, LANs and PBXs have served different functions and have been developed as independent systems. For example, a typical Ethernet LAN simultaneously broadcasts digital data across a shared common bus to all network destinations at data rates up to ten million bits per second (Mbps). Because of the broadcast transport scheme of Ethernet LANs, a number of devices on the network may transmit data simultaneously. Network transmissions are therefore subject to collisions which require the data to be retransmitted. In contrast, a PBX establishes separate dedicated point-to-point connections which are typically operated at lower data rates of only tens of thousand-bits per second (Kbps). Moreover, PBXs must handle the telephony supervision and signaling functions required to interface with the PSTN, and to handle calls within the local telephone network. The real-time event handling and audio distribution required to implement real-time telephony functions are generally inconsistent with the architecture of LANs.
Attempts to integrate PBXs and LANs have been unsuccessful partly due to the increased cost of building a single system which meets the requirements of both networks. In addition to the cost, the functionality and performance of the integrated system is often compromised when compared to separate dedicated systems. For example, providing a PBX with the increased data capacity required by LANs have prohibitively increased the cost of the PBX without delivering the performance provided by dedicated LANs.
A typical office today thus uses two separate and independent networks: a PC LAN to distribute computer data, and a PBX to provide telephone services. The hardware infrastructure of the two networks is independent and separate. Each network requires its own dedicated physical connection medium such as coaxial cable, twisted pair wiring, etc. Traditionally, PBX switching equipment, terminal equipment, control computer resources and in-house wiring are separate devices, not shared or leveraged by the two networks.
The term computer telephone integration (CTI) describes any system which employs a computer to enhance or control telephony. This is implemented by interfacing PBXs and computers, bringing caller information to the computer so database lookup and screen pops to the called agent are possible. Other implementations utilize separate servers with new buses to add voice processing capability. Recently, CTI developers have developed equipment which, when added to a standard PC, allows the functions of a PBX to be implemented. The same PC which operates on the LAN may now also be used to implement the PBX.
Despite the integration afforded by CTI, artifacts of the different development of PBXs and LANs remain. Although the PBX and LAN may be implemented by a standard PC, and may even physically reside within the same device, the two networks remain separate and independent systems. The LAN continues to use its own data transport protocol and physical connection media to each device on the network. The PBX uses its telephony signaling scheme, switching equipment, and separate dedicated physical connection media to transmit voice data.
More recently, ATM (asynchronous transfer mode) networks have been envisioned to integrate digital data with multimedia voice and video onto a single high speed line or "pipe". ATM packages and transmits digital data in small 53 byte fixed-length messages or cells while providing high bandwidths of 25 Mbps and higher. Although ATM networks were envisaged to provide transport of data, voice and video, little has been done to facilitate the transmission of real-time, low latency voice traffic on ATM local area networks. ATM voice transmission efforts to date have primarily been focused on higher-capacity wide area networks, campus backbones and longer haul transmission networks.
The ATM forum has developed ATM standards for local area networks. A great strength of ATM is the ability of the network to assign an appropriate quality of service (QoS) class to a particular transmission. ATM networks can guarantee that strict requirements on available bandwidth and minimal delay can be guaranteed for those connections requiring predictable service. This makes reliable voice transmission possible over an ATM network. Although the bandwidth requirements for voice are easily met by other local area networking technologies, ATM can today provide the predictable quality of service required for real-time bi-directional communication.